The present invention relates generally to variable power telescopic sights having a side-mounted focus adjustment knob and, in particular, to such a sight having a side-mounted focus adjustment knob including a spiral cam mechanism for increasing the focus travel of the sight.
BACKGROUND OF THE INVENTION
Telescopic sights for rifles typically include eyepiece and objective lenses positioned at opposite ends of a tubular housing. Conventional variable optical power telescopic sights also include an erector lens positioned medially of the eyepiece and objective lenses and movable along a central longitudinal axis of the housing for adjustment of the optical power.
In these sights, an image focus adjustment compensating for variations in the distance from the marksman to the target is typically accomplished by longitudinal movement of the objective lens. One prevalent image focus adjustment implementation uses a threaded mounting ring that is coupled to the housing for rotation about the objective end of the housing. The marksman rotates the mounting ring, to adjust the position of a focusing element of the objective lens along the longitudinal axis of the housing.
This implementation is prone to image distortion caused by tilting of the objective lens during focus adjustment and makes it difficult to seal the ends of the housing to maintain within the telescopic sight a nitrogen gas charge necessary to prevent fogging and condensation on internal lens surfaces. This implementation also requires the marksman to stop viewing the target through the telescopic sight, move the rifle out of shooting position, and rotate the rifle to read markings on the outside of the housing or focusing ring which indicate the amount of focus adjustment. After viewing the focus ring adjustment indicator markings, the marksman then must reacquire the target.
A technique for varying the optical power of a telescopic sight is described in U.S. Pat. No. 3,058,391 of Leupold. This telescopic sight has an erector lens positioned between an objective lens and an eyepiece lens and adjustable along the longitudinal axis of the housing. It includes a field lens or collector lens located between the objective and the erector and movable in conjunction with and relative to movement of the power varying erector to compensate for focus effects resulting from movement of the erector. Movement of the collector and erector lenses to maintain focus during adjustment of the optical power of the telescopic sight is accomplished by turning a single adjustment ring concentrically mounted around the housing near the eyepiece end of the sight and connected to a cam sleeve mechanism within the interior of the sight housing.
Because bullet trajectory, wind conditions, and distance to the target can vary depending upon shooting conditions, quality rifle sights typically provide a mechanism for compensating for variations in these parameters by allowing the marksman to make small adjustments to the optical characteristics or the aiming of the sight relative to the rifle on which it is mounted. These adjustments are known as windage and holdover and are typically accomplished by lateral movement of the reticle within the telescopic sight, as shown in U.S. Pat. No. 3,058,391 of Leupold, or pivotal movement of lenses mounted to a pivot tube within the housing to divert the optical path of the observed light before it reaches the reticle, as shown in U.S. Pat. Nos. 3,297,389 and 4,408,842 of Gibson. In these designs, a marksman accomplishes adjustment of windage and holdover by turning a laterally protruding screw or turret that is operatively connected to the reticle or pivot tube. The range of adjustment for windage and holdover in these designs is limited by the space available within the housing for lateral movement of the reticle or pivotal movement of the pivot tube.
Variable power telescopic sights with side-mounted focus control knobs have recently been developed. These sights typically use the erector assembly and cam-sleeve mechanism to vary the power of the sight in accordance with the teachings of U.S. Pat. No. 3,058,391. To facilitate a side-mounted focus control knob, the objective lens system is split into two components, a fixed objective lens portion located at the objective end of the housing and a movable objective lens portion slidably mounted within the housing medially of the fixed objective and the erector assembly. The focus control knob protrudes laterally from the outer side of the sight housing opposite the windage adjustment turret and is mechanically coupled to the movable objective lens portion for adjusting the focus of the sight.
One known embodiment of the focus control knob is described in U.S. Pat. No. 4,643,542. This focus control knob includes an offset drive pin projecting within the interior of the housing and arranged so that rotation of the focus control knob results in orbital movement of the offset drive pin in a plane perpendicular to the axis of rotation of the focus control knob. The offset drive pin is engaged in an elongated slot formed in a link arm. The link arm is located within the interior of the housing and connected to the movable objective lens portion. The slot is oriented transversely of the longitudinal axis of the housing. The coupling between the offset drive pin and the link arm is such that orbital movement of the offset drive pin imparts movement to the movable objective lens portion along the longitudinal axis. One shortfall of the offset drive pin mechanism is that it results in movement of the movable objective lens portion at varying rates depending upon the position of the focus control knob. Because the offset drive pin moves orbitally, it moves along the longitudinal axis quickly when the adjustment knob is in the middle of its rotation, i.e., when the offset drive pin is near the top of its orbital arc, and slowly when the adjustment knob is near either limit of its 180 rotation.
An object of the invention is, therefore, to provide a telescopic sight having a side mounted focus control knob that allows an observer to adjust the focus of the sight and view a readout of the focus adjustment from the observing position without interrupting observation of the target through the sight.
Another object of the invention is to provide such a telescopic sight in which the side-mounted focus control knob includes a spiral cam mechanism that moves a movable objective lens portion longitudinally within a housing of the sight.
A further object of the invention is to provide such a focus control knob that rotates more than 180 degrees in response to which the movable objective lens portion moves with a predetermined longitudinal movement profile.
Yet another object of the invention is to provide a focus control knob for rifle-mounted telescopic sight that is of simple and rugged construction and is capable of withstanding without degradation of accuracy or precision the handling and environmental conditions to which hunting and military rifles are exposed.
These and other objects and advantages of the invention are accomplished in a telescopic sight that includes an elongate tubular housing that holds at opposite ends an objective lens system and an eyepiece lens, a manually adjustable movable erector lens for varying optical power, and a side mounted focus control device located medially along and protruding laterally from the outside of the housing for focusing the sight. The erector lens is located medially of the objective lens system and the eyepiece and pivotally mounted to a pivot tube within the housing to provide for windage and holdover adjustments made by manually adjustable aiming control devices.
In one type of telescopic sight, the objective lens system is split to facilitate side-mounted focus control and includes a fixed objective lens portion positioned at an objective end of the housing and a movable objective lens portion positioned inside the housing medially of the fixed objective lens portion and the erector. The fixed objective lens portion is fixedly mounted within the interior of the housing at one end to form an air tight seal for maintaining a nitrogen gas charge within the telescopic sight to inhibit fogging and condensation on internal lens surfaces. The movable objective lens portion is located in proximity and is linked to an adjustable side-mounted focus control knob that a marksman turns to move the movable objective lens portion along a central longitudinal axis of the housing and thereby adjust the focus of the telescopic sight.
The focus control knob of the present invention includes a cam hub mounted to the housing for rotation about an axis of rotation. The cam hub includes a drive face positioned facing the interior of the housing and a spiral cam track formed in the drive face around the axis of rotation and spiraling outwardly from the axis of rotation. An actuator slide positioned between the cam hub and the housing of the sight includes a cam follower slidably engaged with the spiral cam track. In one embodiment, the spiral cam track is a spiral groove and the cam follower includes a pin sized to fit within the spiral groove. In an alternative embodiment, the spiral cam track is a spiral ridge or rail and the cam follower is a notch or fork including a slot sized for engaging with the spiral ridge. The actuator slide is slidably mounted to the housing and rotatably constrained so that it slides generally along the longitudinal axis of the housing as the cam follower slides along the spiral cam track in response to rotation of the cam hub. A linkage connects the actuator slide to the movable objective lens portion so that the movable objective lens portion moves therewith. The movement profile of the movable objective lens portion, relative to rotational movement of the focus control knob, is controlled by the curvature of the spiral cam track. The arcuate angle or xe2x80x9cturnsxe2x80x9d of the spiral cam track limit the amount of rotation of the focus control knob. A greater arcuate angle covered by the spiral cam track will allow more rotational motion of the focus control knob and, consequently, finer and more precise adjustment of the focus of the sight. More turns of the spiral cam track also dictates that its curvature will be more circular, which prevents rifle recoil from altering the sight""s focus setting.
In another aspect of the invention, the spiral cam track may be of a length that allows rotation of the focus control knob more than 180 degrees. By increasing the amount of rotation of the focus control knob, the resolution of the focus adjustment can be made finer and more precise. It is also possible to design the spiral cam track so that the focus control knob rotates more than 360 degrees. Thus, for example, spiral cam tracks may be formed to have an arcuate angle covering 2, 3, 4, 5 or more turns, and any intermediate angular amount. The size of the spiral cam track is limited only by the size of the drive face and the physical constraints of the materials from which the adjustment mechanism is formed.
In a further aspect of the invention, the focus control knob includes a dial turret with exterior markings that indicate the amount of focus adjustment. This feature enables the marksman to use one eye to view the target through the telescopic sight and the other eye to read the dial turret focus indication markings without moving the rifle from the shooting position.
In still another aspect of the invention, a spring biases the actuator slide relative to the housing to prevent the focus of the scope from changing during rifle recoil.
In yet another aspect of the invention, the spiral cam track may be selected from a right or left-handed spiral to accommodate right-handed or left-handed adjustment mechanisms. The cam hub may include multiple spiral cam tracks all centered on the same axis of rotation, but interleaved. Multiple spiral cam tracks allow a single cam hub to be used to drive actuators for different telescopic sights, requiring different spiral cam curvature and adjustment profiles.